1. Field of the Invention
The invention relates to a tester for an electronic engine control system to check an electronic engine control system mounted on a vehicle.
2. Description of the Prior Art
In recent years, the remarkable proliferation of automobiles has resulted in serious environmental problems. The exhaust gas from the great number of automobiles presents a serious social problem of enviromental pollution. Additionally, limited energy resources require automobiles to run efficiently.
With such a background, a recent effort in this field has been devoted to the development of automobiles equipped with electronic engine control system to electronically control the engine exhaust system, the engine ignition system, the engine intake system and the like for solving the above-mentioned problems.
Referring to FIG. 1, there is shown in block form the interconnection of the components of a conventional electronic engine control system, such an engine system, a computer for controlling the engine control system, an exhaust system for recycling exhaust gas and an output system for providing torque from the engine system. Fuel 12 is supplied to an engine system 11, together with a throttle position signal 13 for adjusting the amount of the fuel 12. The engine system 11 supplies a pressure signal 14 representing pressure in the engine system, a temperature signal 15, and an RPM signal 16 to the computer 17. Upon receipt of the various signals from the engine system, the computer 17 delivers a spark advance signal 18 to the engine 11 for determining when the engine is ignited on the basis of the signals from the engine system. Exhaust gas 19 is fed through path 20 to the engine system 11 and is recirculated through this path. The amount of the recirculating gas is adjusted by an exhaust gas recirculation valve (referred to as an EGR valve) 21. That is, the EGR valve 21 delivers an EGR valve position signal 22 to the computer 17. Responsive to this signal, the computer 23 delivers an EGR valve command signal 23 to the EGR valve 21 to control the EGR valve 21. Torque generated by the engine is transferred through a drive train 25 to cause vehicle motion.
The electronic engine control system as mentioned above has been described, for example, by R. H. Temple and S. S. Delin, Vehicle Control Dept., Ford Motor Co., Dearborn, Mich. U.S.A. in an article "The Use of Microprocessors as Automobile On-Board Controllers" in Microprocessor Applications in 1974 IEEE Intercon Technical Papers presented at the Institute of Electrical and Electronics Engineers International Convention and Expression, Mar. 26-29, 1974.
The block diagram of the automobile on-board controller is illustrated in FIG. 2.
As shown, this example employs a 12-bit word microprocessor for a central processing unit (CPU) 31. Analogue signals 32 from a vehicle are fed to the CPU 31, through a multiplexer/A-D converter 33. In the CPU 31, the control information is calculated on the basis of given algorithms stored in a read-only memory (ROM) 34. A spark system 35 and an EGR system 36 generate a spark timing control signal and an exhaust gas recirculation valve control signal.
The criteria in exhaust gas regulation have been more strict with the years. Further, there is a consistent demand to improve both the fuel consumption and the safety of vehicles. For this reason, the specification of the electronic engine control (EEC) system changes and is more strict year by year.
As a result more sophistcated automobile on-board controllers have been developed. One of them is an electronic engine control module (referred frequently to as an EEC system) 40 (FIG. 3) manufactured by Tokyo Shibaura Electric Co., Ltd. This system 40 executes fuel injection control in addition to spark timing control and exhaust gas recirculation valve control, through the automobile on-board computer 17. These controlled factors are controlled to be optimum for various conditions such as warming up, highland running, urban running, highway running, and maximum-powered running.
Turning now to FIG. 3, analogue input signals 41 derived from various kinds of sensors are delivered to a CPU 43, through a multiplexer/A-D converter 42. A speed signal and a position signal from the engine is transferred to the CPU 43, through a speed/position system 44. A corrected value stored in a read only memory (ROM) 45 is delivered to the CPU 43. The data are calculated on the basis of given algorithms through a microprogram stored in the ROM 45. The result of the calculation is transferred to an EGR control system 46, a fuel system 47 or a spark system 48 to execute the spark timing control, the exhaust gas recirculation control, and the fuel injection control.
Sensor signals inputted into the EEC system 40 and control signals for the sensor signals inputted have meanings as defined below.
In the sensor signals,
PWR (POWER) signal: signal for power supply from a main power supply.
CP+ (CRANK SHAFT POSITION): signal to indicate the crank shaft positions at the + side from a zero point.
CP- (CRANK SHAFT POSITION): signal to indicate the crank shaft positions at the - side from the zero point.
PCR (POWER CRANK): signal to indicate whether the engine is in starting condition or in running condition.
SIGRTN (SIGNAL RETURN): answer back sense signal for all the sensors.
CAT (CARBURETOR AIR TEMPERATURE): signal to indicate the temperature of air intaken into a carburetor.
BP (BAROMETRIC PRESSURE): signal to indicate ambient pressure at highland running.
TAP (THROTTLE ANGLE POSITION): signal to indicate the position of a throttle.
ECT (ENGINE COOLANT TEMPERATURE): signal to indicate the temperature of coolant.
EVP (EXHAUST GAS RECIRCULATION VALVE POSITION): signal to indicate the position of the exhaust gas recirculation valve position.
MAP (MANIFOLD ABSOLUTE PRESSURE): signal to indicate the pressure of a manifold.
AFR (AIR FUEL RATIO): signal to indicate the mixture ratio of fuel to air.
IAT (INTAKE AIR TEMPERATURE): signal to indicate the temperature of new charge in an intake manifold.
In the control signals,
SPOUT (SPARK OUT): signal to control the timing of spark.
VREF (REFERENCE VOLTAGE): signal to make signals with various levels for comparing them with an analogue signal.
SAD (SECONDARY AIR DUMP): signal for indicating whether the secondary exhaust gas control is conducted or not, that is to say, whether the primary exhaust gas is recirculated or not.
EGRP (EXHAUST GAS RECIRCULATION PRESSURE SOLENOID): output signal for the pressure solenoids of power devices such as a power window and a power brake.
CANP (CANNISTER PURGE): signal used in a solenoid system. For example, in a four cycle engine operating through four strokes, leakage gas between the cylinder and the piston in the compression stroke is not exploded in the explosion stroke. This signal is used to drive a solenoid for feeding again the leakage gas into the combustion chamber.
The algorithm and corrected value as mentioned above varies depending on the kind of car. For this, the EEC system in this example employs the ROM 45 of a module type in which a desired module of ROM may selectively be used in accordance with the kind of car used. In this specification, the read only memory will be referred to as a calibration assembly.
When such a control system is mounted on an automobile, new problems arise. One of them is how to check the perfectness of the function of the EEC system and how to simply and correctly trouble-shoot the system. This necessitates a tester to correctly diagnose the electronic engine control system in a simple manner.